Process for the destruction of foam

Abstract

The invention relates to the destruction of foams that are produced in various industrial processes, especially in the degassing and/or removal of monomers from plastics dispersions, by the use of porous filter elements without using moving mechanical foam-destroying devices and/or without the addition of chemical foam-destroying agents.

We claim: 
     
       1. A process for the destruction of foam produced during the removal of residual monomers from an aqueous polymerizate dispersion having a tendency to foam consisting essentially of passing the gases being removed containing residual monomers through porous filter elements constructed of sintered materials and having a dimension of from 0.5 to 40 m 2 , a porosity of from 15% to 85% and a maximum pore size of from 1 to 500μ, at such a rate that the difference in pressure through the filter elements does not exceed 25% of the original pressure, whereby foam in contact with said filter elements is destroyed, and the liquid portion of said destroyed foam is returned to said aqueous polymerizate dispersion. 
     
     
       2. The process of claim 1 wherein said porous filter elements have a porosity of from 25% to 50% and a maximum pore size of from 5 to 100μ. 
     
     
       3. The process of claim 1 wherein said porous filter elements have at least two layers where the first layer in the direction of flow has a smaller pore size than the following layers. 
     
     
       4. The process of claim 3 wherein said porous filter elements having at least two layers are filter candles. 
     
     
       5. The process of claims 1 or 3 wherein said porous filter elements are constructed of sintered stainless steel. 
     
     
       6. The process of claims 1 or 3 wherein said polymerizate dispersion is treated with water vapor. 
     
     
       7. The process of claims 1 or 3 wherein said aqueous polymerizate dispersion is an aqueous polyvinyl chloride dispersion and said residual monomer gases are monomeric vinyl chloride. 
     
     
       8. A process for the destruction of foam produced during the removal of gases from an aqueous vinyl chloride polymer dispersion containing residual monomeric vinyl chloride prepared by emulsion, suspension or microsuspension polymerization conditions, consisting essentially of degassing said dispersion at temperatures of from 50° to 100° C. at a pressure of from 5 bar absolute to 0.3 bar absolute, passing the gases being removed through porous filter elements constructed of sintered materials and having a dimension of from 1 to 15 m 2 , a porosity of from 25% to 50% and a maximum pore size of from 5 to 100μ, in such a controlled manner that the difference in pressure through the filter elements does not exceed 25% of the original pressure, whereby foam in contact with said filter elements is destroyed and the liquid portion of said destroyed foam is returned to said aqueous vinyl chloride polymer dispersion.